1. Field Of The Invention
The present invention relates generally to a delay circuit for delaying analog signals, and more particularly to a delay circuit provided with one or more semiconductor devices arranged in a large scale integrated circuit.
2. Description Of The Related Art
A phase shifter has been utilized as a conventional delay circuit in which analog signals ranging over all bands are delayed without decreasing the amplitude of the analog signals. The phase shifter is generally provided with constructional elements such as a plurality of operational amplifiers, a plurality of resistors, a plurality of capacitors, and the like. The constructional elements are integrated on a large scale. For a detailed description on the conventional delay circuit, see Japanese Patent Application No. 65749 of 1980 laid open to public inspection on Dec. 12, 1981 under Provisional Publication no. 161711/81, and N. Fujii, 37 Design of Operational Amplifier", a series of Electro-Science 74, published by Sanpoo in Japan.
The operational amplifiers in the conventional delay shifter is important to delay the analog signals. Also, three of more transistors are connected to each other in series between an electric source terminal and ground in the conventional delay shifter to change frequency characteristics of the amplitude of the analog signals in dependence on the frequency of the analog signals.
Therefore, the transistors arranged in series can not be operated on condition that an electric potential of the electric source terminal is equal to or less than 3 V. In other words, an electric potential range (or, a dynamic range) allowed for the analog signals is not enough to delay the analog signals in the conventional delay shifter. Also, noise generated in the conventional delay shifter is amplified in a series of transistors.
Accordingly, in cases where the electric potential of the electric source terminal is low, the phase shifter can not utilized as the conventional delay circuit.
2.1. Previously Proposed Art
A conventional delay circuit in which a low electric potential is applied to an electric source potential to delay an analog signal has been recently used.
FIG. 1 is a circuit diagram of a conventional delay circuit in which a low electric potential is applied to an electric source potential to delay an analog signal.
As shown in FIG. 1, a conventional delay circuit 11 is provided with a first resistor R.sub.11 of which one end is connected to an electric source terminal 12, an npn type of transistor Q.sub.11 of which a collector is connected to another end of the first resistor R.sub.11 and a base is connected to an input terminal 13, a second resistor R.sub.12 of which one end is connected to an emitter of the transistor Q.sub.11 and another end is grounded, a capacitor C.sub.11 of which one end is connected between the first resistor R.sub.11 and the transistor Q.sub.11 and another end is connected to an output terminal 14, and a third resistor R.sub.13 of which one end is connected between the second resistor R.sub.12 and the transistor Q.sub.11 and another end is connected to the output terminal 14.
In the above configuration, a sinusoidal analog signal is transferred from the input terminal 13 to the base of the transistor Q.sub.11 as an input signal. Thereafter, the analog signal is amplified in the transistor Q.sub.11 and is delayed in the delay circuit 11 by coaction of the resistors R.sub.11, R.sub.12, R.sub.13 and the capacitor C.sub.11 before the analog signal delayed is output from the output terminal 14 as an output signal.
In this case, because the transistor Q.sub.11 and the resistors R.sub.11, R.sub.12 are only arranged between the electric source terminal 12 and ground, the analog signal is reliably amplified and delayed in the delay circuit 11 even though the electric potential of the electric source terminal 12 is less than 3 V.
Also, in cases where the forward current gain h.sub.fe of the transistor Q.sub.11 is large enough and in cases where stray capacitance which is, for example, generated between lines is small enough, the analog signal passes through the delay circuit 11. In addition, in cases where a resistance of the first resistor R.sub.11 equals a resistance of the second resistor R.sub.12 and in cases where a resistance R of the third resistor R.sub.13 is larger enough than an emitter resistance r.sub.e of the transistor Q.sub.11, the analog signal passes through the delay circuit 11 without decreasing an amplitude of the analog signal even though the frequency of the analog signal belongs in any band. In other words, analog signals ranging over all bands can pass through the delay circuit 11. Therefore, all-pass characteristics is exhibited in the delay circuit 11.
In this case, a transfer function H.sub.o (.omega.) of the delay circuit 11 defined as a ratio of a Laplace transformed output function Y.sub.o (.omega.) of the output signal to a Laplace transformed input function X.sub.o (.omega.) of the input signal is formulated according to an equation (1). EQU H.sub.o (.omega.)=(1-j.omega.RC)/(1+j.omega.RC) (1)
Wherein, the symbol j denotes an imaginary number, the symbol .omega. denotes an angular frequency of the analog signal, the symbol R denotes a resistance of the third resistor R.sub.13, the symbol C denotes a capacitance of the capacitor C.sub.11, and the symbol r.sub.e denotes the emitter resistance r.sub.e of the transistor Q.sub.11.
A delay time function Td.sub.o (.omega.) denoting delay time characteristics of analog signals ranging over all bands is determined by utilizing the equation (1). EQU Td.sub.o (.omega.)=2RC/{1+(.omega.RC).sup.2 } (2)
Specifically, a low band delay time Td.sub.o in a low band (1&gt;&gt;.omega.RC) is EQU Td.sub.o =2RC (3)
2-2 PROBLEMS TO BE SOLVED BY THE INVENTION
However, constants R, r.sub.e, and C in the transfer function H.sub.o (.omega.) depend on the constructional elements of the delay circuit 11 so that all of the constants R, r.sub.e, and C are fixed. That is, the transfer function H.sub.o (.omega.) only depends on the angular frequency .omega. of the analog signal.
Accordingly, it is difficult to change the transfer function H.sub.o (.omega.), independent of the angular frequency .omega. of the analog signal. Therefore, a delay time such as the low band delay time Td.sub.o can not be adjusted as required, independent of the angular frequency .omega. of the analog signal.